1. Field of the Invention
The present invention relates to an interlaced-to-progressive conversion apparatus and method using motion and spatial correlation. More particularly, the present invention relates to an apparatus and method for converting an interlaced image signal into a progressive image signal by interpolating spatially or temporally depending on motion and spatial correlations.
2. Description of the Related Art
Generally, an interlaced-to-progressive conversion (IPC) device has widely been used for reducing many artifacts due to interlaced scanning, namely, deterioration of vertical resolution, flickering of a scanning line, and the flickering of a wide area in systems such as NTSC, PAL, SECAM, etc.
Recently, the interlaced-to-progressive conversion apparatus has become more important since a high definition (resolution) television (HDTV) system adopts a plurality of standards on signal formats and the conversion among standard input/output signals of various formats is required frequently.
The interlaced to progressive conversion algorithm which have been developed in an early stage was intended for systems such as NTSC, PAL, SECAM, etc. Various algorithms which have been proposed are commonly based on an interpolation for reproducing the lines which are excluded in the interlaced scanning.
An algorithm proposed to reduce such artifacts, an interpolating method according to a simple line doubling, vertical filtering, and a method based on vertical edge information are disclosed in a first reference: D. I. C. Hentschei, "Comparison Of Median Filtering and Vertical Edge Controlled Interpolator for Flicker Reduction," IEEE Trans. on Consumer Electronics, vol. 35, no. 3, pp. 279-289, August 1989.
An interpolating method according to an edge direction is disclosed in a second reference: D. Bagni, R. Lancini, S. Landi, and S. Tubaro, "HD-TV Spatio-temporal Upconversion," Proc. of the Int. Workshop on HDTV, 1994.
A non-linear high-speed interpolating method based on a weighted median filter is disclosed in a third reference: J. Juhola, A. Nieminen, J. Salo, and Y. Neuvo, "Scan Rate Conversion Using Weighted Median Filtering," Proc. IEEE ISCAS-89, Portland, USA, May 1989, pp. 433-436.
An algorithm based on an FIR median hybrid filter is disclosed in a fourth reference: A. Lehtonen and M. Renfors, "Non-linear Quincunx Interpolation Filtering," Proc. SPIE's Visual Communication and Image Processing, Lausanne, Switzerland, October 1990, pp. 132-135.
An algorithm based on a complementary median filter is disclosed in a fifth reference: H. Blume, L. Schwoerer, and K. Zygis, "Subband Based Upconversion Using Complementary Median Filter," Proc. of the Int. Workshop on HDTV, 1994.
An algorithm based on median filtering according to a direction is disclosed in a sixth reference: T. Doyle, "Interlaced to Sequential Conversion for EDTV Applications," pp. 421-430, Signal Processing of HDTV, L. Chiariglione Ed., Elsevier Science Publishers, North Holland, 1988.
Algorithms based on a vertical-temporal median filter are disclosed in seventh and eighth references: P. Frenchen, "Two Integrated Progressive Scan Converters," IEEE Trans on Consumer Electronics, vol. 32, no. 3, pp. 237-240, 1986; and T. Doyle and P. Frencken, "Median Filtering of Television Images," IEEE Digest of Technical Papers, pp. 186-187, 1986.
Also, motion adaptive schemes are disclosed in ninth and tenth references: N. Suzuki and et al, "Improved Synthetic Motion Signal For Perfect Motion-Adaptive Pro-Scan Conversion in IDTV Receivers," IEEE Trans. on Consumer Electronics, vol 33, no. 3, pp. 266-271, August 1989; and C. P. Markhauser, "Motion Adaptive Pro-Scan Converter with Two Dimensional Contour Enhancement," IEEE Trans. on Consumer Electronics, vol. 36, no. 2, pp. 110-114, May 1990.
The above interlaced-to-progressive conversion methods can roughly be categorized into a spatial-interpolating method, a temporal-interpolating method, and a three-dimensional interpolating method which combines the spatial-interpolation and the temporal-interpolation.
In the three-dimensional interpolating method, it is important to detect a motion in the image and carry out a temporal-interpolation appropriately on the basis of the detected motion since a wrong temporal-interpolation can cause deterioration of picture quality, such as a tearing-artifact. This is due to the fact that the maximum temporal frequency which can be determined theoretically is limited since a temporal sampling rate is smaller than a Nyquist rate in a real image signal.
However, it is possible to enhance the reliability of motion information by using the spatial information of a sample along with the motion information together, as proposed in the present invention.